Process for the recovery of phenols from gas liquors



Jan. 29, 1935. w. TIDDY '1,989,177

PROCESS FOR THE RECOVERY OF PHENOLS FROM GAS LIQUORS Filed May 20, 1931 2 Sheets-Sheet 1 MMM. I f

.1m/Maisy :ul/72 @D `Ian. 29, 1935. W, TlDDY 1,989,177

PROCESS FOR THE RECOVERY OF PHENOLS FROM GAS LIQUORS Filed may 2o, .1931 2 sheets-sheet 2 .ca/00.930 ,Qn/vanaaf ,//ofuarag 24a/7 i l INVENTOR /4//7//4/77 770%] ATTORN EY Patented Jan. 29, 1935 UNITED vsmi-ifrlssam l PROCESS Fon THE RECOVERY or rHENoL letti FROML GAS LIQUORS i William Tiddy, Scarsdalle, N.`"VY., assigner to Semet-Solvay Engineering Corporation, New York, N. Y., a corporation of New Yorlr Application May 20, 1931, Serial No. 538,738

4 Claims.' (ci. 26o- 154) 5 liquors of coke ovens and gas Works.

One obj ect of this invention is to provide a process for recovering, economically and eiciently, substantially all of the phenols from gas liquors containing same.

Another object of this invention is to condition gas liquors which, in addition tophenols, contain carbon dioxide, hydrogen sulfide, and ammonia both in the free and iixed form, so as to remove constituents which react with the reagents util lized in accomplishing the removal of phenolsv prior to treating such liquors to remove phenols therefrom, and hence, conserve the phenol removing reagents vvhich otherwise Would be lost to the system.

The presentv invention is directed to a process for recovering organic compounds, such as tar acids, from Waste and gas liquors and involves, first, removing components from the liquor, such as free ammonia, hydrogen sulfide, and carbon dioxide, and thereafter contacting the liquor with a suitable extracting agent, as for example, light oil, neutral tar oils or benzol, reconditioning the extracting agent by means of an alkali or other treatment and recovering the fixed ammonia from the phenol-free liquor by treating this liquor. With lime or other alkaline material followed by a distillation step. l

Weak liquors from coke ovens and gas Works contain, among other constituents, a considerable v amount of carbon dioxide, hydrogen sulfide, and free and fixed ammonia, together with varying percentages of phenols. It has been proposed to remove the phenols from such liquors by extracting them with light oil or other extracting agents, such as benzol, thereafter reconditioning the extracting medium by a caustic or other alkali treatment and recovering the phenols byacidifying the alkali phenolate separated from the extracting medium. Waste liquors have been treated in this manner prior to the steam distillation thereof to recover free and xed ammonia contained therein. The treatment of such liquors before distillation for the recovery of ammonia has the advantage that it materially reduces the amount of liquors to be treated, since the liquors coming from the ammonia'still are much greater in amount due to the addition of moisture by condensation of steam Within the still. Further, theV liquors coming from the stilll` contain limel added thereto in the lime leg, which reacts with the phenols to form` calciumy phenolates. I have found that phenols from the ammonia still cannot be eiliciently extracted, presumably due to'the lime treatment of the liquor the xedleg' of the still' to liberateammonia.

In the extraction of the liquors, the extracting medium, in addition to. absorbing the phenols, also takes up a considerable portion ofthe carbon`v dioxide, hydrogen sulde, and other impurities soluble in the extracting medium, present inthe 1050 liquor. jUpon subsequent. treatment of the phenol-extracting agent withcaus'tic, the hydrogen sulde, carbon dioxide,y and other impurities, taken kup by the extracting agent, react with the caustic,iconsequentlymaterially increasing the amount of caustic necessary for the practiceof the process.

In the usual process'of treating gas liquor, the liquid is introduced cold into theftop of the ani-'-v monia still and passed down therethrough, substantially all of the free ammonia being driven off in its passage 'through the.l free leg oflthev still. The liquor is then passed into the lower part 'of the still Where it comesinto contact with lime in what is known as the lime leg. The lime frees any ammonia which may be present in combined form.A The liquor containing this free ammonia is then passed into the iixed leg of the still Where the ammonia is driven ou, passing up intothe free leg of the'still. The ammonia vfrom'the still may be passed into distilled Water, Where it isfab-A sorbed and produces aqua ammonia solution. If ammonium sulfate or othersalt is desired,fthe ammoniagas is passed through asaturator containing sulfuric or other acid to formthe desired salt.

If phenols have notbeen removed from the gas liquor before treatment 'to recover ammonia, the Waste liquor coming from the bottom of the still will contain substantial quantities of phenol. In; view of the phenol content of suchvvaste liquor, the discharge thereof into streams would be destructiveto the flora and fauna contained therein.

In accordance with the preferred embodiment of the present inventionthe Weak liquors containing phenols and other constituents, such a's` the liquors from coke oven plants or gas Works, are iirst preheated and then introduced intothe free ammonia still, wherein the freel ammonia, carbon Idioxide, and hydrogen sulde are removed; The temperature of the vapors coming oi from theitop of the"` still ispreferablymainf tained Within a range of fromz93 to 98",v C.,and preferably at a temperature of approximatelyv 95; C. The top of the still is continuously cooled by` 20 to 65 C., preferably by heat interchange with the liquor fed to the ammonia still. Thereafter the cooled liquor is extracted with' Va suitable phenol absorbing medium, such as light oil. In

accordance with one form of this invention, the extraction of phenols is accomplished by vigorously mixing the light oil or other absorbing medium with liquor, preferably by means of centrifugal pumps, and thereafter passing the resultant mixture into decanters where the liquid is separated from the oil. Instead of centrifugal pump extraction of the phenols by means of light oil, above briefly described, the light oil and liquor may pass in continuous counter-current flow through suitable extracting towers.

The phenol-free liquor,` preferably heated by passage'in heat interchange relation with the hot Waste liquors coming from the free ammonia still, is thenk passed into the lime leg or reservoir of the'ammonia still, the fixed ammonia contained in theliquor reacting'with the milk of lime therein; thus liberating ammonia which is removed by distllling the liquor in the fixed leg of the ammonia still.l The waste liquor from the iixed leg ofthe ammonia still, it will be noted, contains substantially no phenols and may be disposed of conveniently.

The light oil or other extracting medium may be processed in the usual manner to recover phenols therefrom, as for example, by treatment with caustic in a scrubbing tower Vand thereafter re-used to extract additional phenols from the free ammonia, carbon dioxide, and hydrogen sulnde free'liquor. The' sodium phenolate formed in thecausticV tower may be vconcentrated and sold as such 'or may be acidifled to form phenols which are puried in any well known manner and constitute a valuable by-product ofthis process.

The light oil used in the practice of this invention may be'the unrened oil obtained at the coke oven plant by treating the gas distillate with a suitable absorbing medium, such as straw oil, and thereafter distilling the resultant benzolyz'edoi'l'tov obtain the crude light oil containing benzaol, toluol, xylol, a small fraction of unsaturated" compounds, i. e., oleflnes, and other constituents. In the accompanyingl drawings, Fig. 1 illustrates a layout ofapparatus adapted to carry out the processherein described, the extraction of phenols from waste liquors, in the showing of this iigure, being accomplished by extractors or absorbers through which the liquor and extractingmedium now in counter-current direction; and

Fig. 2 illustrates a modification of this invention,` the modification chieiiy involving the substitution of a centrifugal pump apparatus for extracting the phenois from waste liquors for the counter-current scrubber apparatus of Fig. 1.

-fReferring to Fig. 1 o1'- the drawings, Areference numeral 1 indicates an ammonia still composed of a free leg- 2, superposed on a fixed leg 3. Free leg 2 is provided,at its top, with a vapor outlet @which Ieadsto the ammonia recovery system (not shown). The still, as customary, is divided into a plurality of sections, the base of each of which is provided with dephelgmating plates and hoods, permitting flow of vapors up through the still'and the downward iioW of reflux liquid and condensate, the vapors in passing up through the still, bubbling through the condensate on the dephlegmating plates. The top section 5 `of the still is provided With a cooling coil 6 through which Water or other liquid may be circulated `to control the temperatures of the vapors leaving Steam is supplied to the still through valvey controlled pipe 9 disposed in the base of the xed leg 3, the steam and vapors removed from the liquor in the fixed leg rising through opening 11 in the base plate l2 of the free leg 2 and commingling with the vapors iiovving through the free leg as will be more fully explained hereinafter.

From the coils 7, the weak liquor is discharged onto the dephlegmating plates, flowing down through the free leg, in direct heat exchange relation with the vapors and steam flowing up through the still, the lower boiling components, such as hydrogen sulfide, carbon dioxide, and free ammonia, being released from the liquor and passing up through the still, leaving it through the vapor outlet 4. lFinally, the Weak liquors from which substantially all the carbon dioxide, hydrogen sulfide, and free ammonia have been removed, reach the base plate 12, from which they pass through pipe 13`into the heat exchanger 14.

The fixed leg 3 of the still is also built up of the usual dephlegmating plate and hood construction. Positioned adjacent the leg 3 is a usual lime leg or reservoir 15, which is connected thereto by pipe 16,'arranged to discharge the lime treated liquor into substantially the top of the xed leg 3. Dephenollzed liquor, i.e., liquor from which the phenols have been removed, is fed from the heat interchanger 14 through pipe 17 into the base of the lime leg 15 and passes up therethrough into and through pipe 16. From this pipe, the dephenolized liquor flows down through the fixed leg in counter-current direction to the flow of steam supplied through valvecontrolled pipe 9. Steam, ammonia, and vapors, driven off from the lime-treated liquor, pass up through leg 3 Vinto and through opening 11 into and through leg 2, as hereinabove described. The ammonia-free liquor leaves the base of the leg 3 through conduit 18 and passes into seal 19, provided with a discharge pipe 21.

The liquor from the free leg 2 of the still, containing fixed ammonia and phenol, but from which carbon dioxide, hydrogen sulfide and free ammonia has been removed, termed phenolized liquor on the drawings, is pumped by means of pump 21 through heat interchanger 14, pipe 22, heat interchanger 23, pipe 24, into'the top of primary extractor 25. Pump 21A forces the phenclized liquor through a series of sprays disposed above tlie level of the extracting medium in the tower 25 so that the liquid, in spray form, contacts with the extracting medium over subtractor 25 and is pumped therefrom by pump 26,

through pipe 27. into the top of secondary extractork 28, which, preferably, is of like construction and design as that of extractor 25. From the extractor 28, the liquor, from which substantially all the phenols have been removed, i. e., the dephenolized liquor, ows, preferably by gravity, through pipe 31 into and through heat exchanger 14,'pipe 17, into the lime leg or reservoir 15. In the heat exchanger 14, the'cold dephenolized liquor passes in indirect heat vinterchange relation with th'e hot phenolized liquor, coming from the free leg 2 of the still 1. .As hereinabove described, lime-treated `*liquor passes from the lime leg into the fixed leg 3 `of the still where the ammonia, liberated bythe lime treatment, is removed. The ammonia-free liquor is'discharged from the base of the still .through discharge pipe 18 into seal 19, from which it flows through pipe 21, connected toa waste line or suitable point of disposal.

VPtu'iled light oil, that is, oil containing substantially no phenols, or other extracting medium is pumped by means of pump 32, through pipe 33 into the secondary extractor 28, rising up through the body of liquor contained therein. The volume of light oil passed through each `extractor is preferably 1.25 timesr that of the liquor. The extracting medium is preferably introduced at a point in the extractor above the level of the liquor, occurring at the base of the extractor, separated from the mixture of oil and Jliquor. The absorbing or extracting medium rrises through the extractor 28, removing the major portion of the phenols from the liquor passed therethrough and then passes out through pipe 34 into the primary extractor 25. Here the absorbing medium, containing phenolsabsorbed in secondary extractor 28, contacts with the incoming liquor containing maximum amountsv of phenols introduced into the primary extractor 25, through pipe line 24 by pump 21', the extracting oil entering the extractor at a level above the layer of liquor in the base of this extractor rising up through the liquor therein and leaving the extractor 25 through pipe line 35. From '75 to 85% of the phenols are removed in the primary extractor and substantially the remainder of the phenols removed in the secondary extractor 28.

Pipe line 35 leads to the base of a caustic soda washer 36. The phenolized light oil rises through the body of caustic in washer 36, continuously leaves this washer through pipe 38 connected to the base of a second caustic washer 39, and rises up through the body of caustic therein. The caustic solution reacts with the phenols in the light oil to form sodium phenolate, which separates from the oil and remains in the caustic solution. The pump 32 forces the dephenolized light oil from the caustic washer 39 through pipe line 41, into the secondary extractor 28, as hereinabove described. The caustic solution originally introduced into the washers 36 and 3'7`contains about 25% by weight of caustic.

When it is desired to replace the caustic in tower 39, the caustic solution is discharged therefrom and fresh caustic solution is pumped Afrom tank 42, by means of pump through pipe line 44, which leads into the top of thev washer 39. If desired, the partially used up caustic solution in tower 39 may be pumped therefrom through pipe 37 into the caustic soda washer 36. It will be understood, of course, that Washers 36 and 39 and associated pipe lines' are provided with suit-1.- able valves to permit simultaneous continuous use of either or'both towersk and to shut off lone of the washers from the system to permit the;

other to operate when it is desired to replace the 1 caustic therein.

Wheny the caustic in the tower 36 has completely reacted with the phenols to form sodium phenolate, it may be discharged therefrom into storage tank 43, from which the sodium phenolate may be withdrawn through pipe line 44 for purication or concentration treatment.

The 'structure and operation ofthe ammonia still,-heat' exchangers and caustic soda washersof Fig. 2 are the same as the corresponding elements of Fig. .1. Accordingly, the correspondingv elements of these two figures. have been given the same reference numerals. A descriptionof .the part'sof Fig. 2 which have already been described in connection with the apparatus of Fig. 1,' is considered unnecessary. f

The chief distinction between the modication of Fig. 2 and that of Fig. 1 resides in the means for accomplishing the removal of phenols from the liquors coming from the free leg of-.thevstill from which liquors carbon dioxide, hydrogen sull' fide,l and free ammonia have. been removed. In accordance with the embodiment of theinvention shownv in Fig. 2, the cold phenolized liquorffro'm' the heat exchanger23 is passed into a-centrifugal pump 51 of any well-known design and which is preferably operated below its capacty.` ylnthi's pump, the phenolized liquor -is contacted'v` and vigorously agitated with light oil or other extracting medium` introduced thereinto through ,pipe line 52, leading from the top of secondary decanter 53.' The resultant mixture is continuously pumped, by means of pump 51, through pipe line- 54 into the primarydecanter 55. y

The partially phenolized light oil and liquor stratify intovtwo layers in primary decanter 55,5

this decanter through pipe line 5'7,A which disi charges into overflow device 58 of pipe 59 com municating with a second centrifugal pump 6l. Purified or dephenolized light oil from the caustic soda washer 39 is passed through pipeline 41 'into the pump 61 where the dephenolized light oil and the liquor. from which the major portion of the phenols has been removed in the preceding pump-. ing and decanting operation, are vigorously agitated and admixed and discharged byl the pump 61 through pipe line 62 into the secondary decanter 53.l In this decanter the light oil or other absorbing medium and liquor stratify'.- The lower dephenolized liquor layer passes through line 64, leading from the base of the decanter into the overilow device 65 communicating with pipe line 66, which leads kto the pump 6'7. The relatively cold dephenolized liquor is pumped by means of pump 67 through pipe line 68 into the heat exchanger 14 where it passes in indirect heat exchange relation with hot phenolized liquor lfrom the free leg 2 of the still 1. From the heat exchanger 14, as above described, the partially preheated dephenolized liquor is passed into the lime leg or reservoir 15. Preferably the-light oil is introduced into the pumps in amount equal t about 1.25 times the volume of liquor. The upper light oil layer containing the phenols removedfingthe secondary decanter` 53, as hereinabove described, passes through pipe 52 centrifugal pump 51.

One .example of operating conditions maintainable in the practice of this process, to which it will be understood this invention `is not confined, is as follows: I

100,000 gallons of Weak ammonia liquor at a temperature of approximately C. enters heat exchanger 23 'and leaves this exchangerv and enters dephlegmator coil '7 at a temperature of approximately C. The liquor leaves the coil.' 7 and enters the free leg of the ammonia still at a temperature of approximately 90 C. I In the free leg of the still, the carbon dioxide andhydr'ogen sulfide are removed from the liquor, which leaves into the the still at ak Vtemperature of approximately 102 C., and at this temperature enters heat exchanger 14.` In passing through the free leg of the ammonia still, the'liquor is augmented'by condensation of steamand other vapors by approximately 12,000 gallons. The liquors leave the exchanger 14 at a temperature of approximately 50 C., enter heat exchanger 23, and Aleave this-exchanger at a temperature of approximately 40. C. At this temperature the'liquor is introduced intothe extractors in which no substantial change in temperature takes place. The light oil extracting medium at a temperature of 40 C. is introduced into, and the dephenolized liquor Aand phenolized light oil Withdrawn from, the extractorsat a temperature of 40 C. 140,000 gallons of light oil are used to treat the 112,000 gallons of liquor `in the-extractors. From the extractors, the liquor passes through heat exchanger 14 and enters the lime reservo-i1' at a temperature of approximately 90 C.

Analyses of the liquor and light oil are as follows:

The Weak liquor entering vthe free leg' of the ammonia still contains 3.6 grams of phenol, 2.7 grams of hydrogen sulfide, and 4.1 grams of'carbon dioxide per liter of liquor. VThe liquor leavingvthe free leg of the still and entering the extractor contains 3.2 grams of phenol, 0.07 grams of hydrogen sulde, and 0.88 grams of carbon 'dioxide per liter of liquor.l The dephenolized liquor leaivng the extractors contains 0.15 grams of phenol, 0.067-grams of hydrogen sulfide-and 0.88 grams of carbon dioxide per liter of liquor. The light oil entering the secondary extractor Where it initially contacts With the weak liquor contains 0.20 grams of phenol'per liter of liquor, and no hydrogen sulfide or carbon dioxide. Upon leaving the extractors, the light` oil contains 2.63 grams of phenol, 0.0024 grams of hydrogen'sulfide, and-0.0008 grams of Acarbon dioxide vper liter of liquor. z

Thus, in accordance with this invention, a phenol recovery of 95% based onthe total phenol content of the liquor is obtainable. Further, the process results in -a saving of 235.2 pounds of sodium hydroxide per .100,000 gallons yof Weak liquor, since if the Weak liquor isnot treated in accordance with this invention, the light oil leaving the extractor Would contain 0.08 grams of hydrogen sulde, and 0.024 grams of carbon dioxide per liter of liquor which Would react Withy 242 pounds of sodium hydroxide per 100,000 gal.- lons of Weak liquor. Due tothe preliminary distillation of the liquor in the free leg of the ammonia still, hereinabove described, the hydrogen suliide and carbon dioxide contents of the light oil, as above indicated, are reduced to 0.0024 and 0.0008 grams, respectively, per liter of liquor, which lreact with only 6.8 pounds of sodium hydroxideper 100,000 gallons of liquor. The difference between 242 and 6.8`pounds' represents the saving of caustic per 100,000 gallons of weak liquor effectedbythe process of this invention.

The. centrifugal pump extracting apparatus preferably operates continuously, the liquor and light oil being continuously introduced thereinto, vigorously 'agitated by the 'blades of 'the pump,continuously discharged into substantially the .midportion of the decanter, the phenolized light oil being continuously withdrawn from the top and the partially orisubstantially totally 4dephenolized liquor, as the case may be, continuously Withdrawn from the bottom of the decanter. Of course, if desired, the decanting koperation may be performed in batches instead of continuously.

, It Will be noted that, in accordance with this invention, thel carbon dioxide, hydrogen sulfide and free ammonia are removed from the gas liquor before phenols are extracted therefrom by means of an extracting medium, such as light oil. After extraction or" phenols, the gas liquor is pass'ed through the lime l'eg to liberate the fixed ammonia, which is recovered by distilling the lime treated liquor in the fixed leg of the still. The Waste liquor from the fixed leg, it Will be noted, is free of phenols, and consequently, may be readily disposed of as such into streams or other Waste lines. Due to the removal of carbon dioxide and hydrogen sulfide before treatment of the liquor with. light oil to remove phenols, carbon dioxide and hydrogen sulfide contained in the liquor are not taken up by the light oil and consequently, the amount of caustic necessary for treating the light oil to remove phenols therefrom is materially reduced. Further, due to ythe 'treatment of the liquor to remove phenol before treatment thereof with lime to liberate the iixed ammonia, the dimculties encountered in the treatment of the lime-treated gas liquors are obviated.

It Will, of course, be understood that while specific embodiments of the invention have been described,l Various changes in the details thereof might be made by those skilled in the art and this inventionis not to be limitedto the disclosure herein, but only by the scope of the appended claims. I

I claim:

1. The improvement in the process of extracting liquors containing phenols and other constituents which react with alkali, which process involves extracting the'phenols from said liquors with an inert organic extracting medium and thereafter treating the extracting medium containing the phenols to form water soluble phenolates, said other constituents being soluble in the inert organic extracting medium, which comprises iirst removing said other constituents from the liquors While retaining the phenols therein, then extracting the liquors with said inert organic extracting medium to remove the phenols therefrom, and treating the phenolized extracting medium with alkaline material to recover the phenols contained said extracting medium.

2. The process of recovering phenols from gas liquor containing phenols, hydrogen sulfide, carbon dioxide, and free ammonia, which comprises distilling the liquor at such temperature as to drive off substantially all of the hydrogen sulfide, carbon dioxide and free ammonia, While retaining the phenols, cooling the resultant liquor from the distillation treatment, extracting the cooled liquor with an inert organic solvent, thus removing the phenols therefrom, and treating the Vdistilling the liquor in a dephlegmator column` .While cooling the vapors leaving the column so that the temperature thereof does not exceed 98 C., thus driving ofi the free ammonia, hydrogen sulde and carbon dioxide, While retaining the phenols in the liquor, cooling the resultant liquor from this distillation treatment, extracting the cooled liquor With an inert organic solvent to remove the phenols therefrom, and treating the phenolized extracting medium with caustic to recover the phenols.

4. The process of treating gas liquor containing phenols, hydrogen sulfide, carbon dioxide, and

'free and fixed ammonia and in Which the fixed ammonia is recovered after the removal of the phenols from the gas liquor, the steps which comthe purified light prise (1) passing the liquor through the free leg of an ammonia still, the top of which is cooled by circulating liquor therethrough so that the vapors leaving the still are at a temperature not exceeding 98 C., thus removing substantially all hydrogen sulde, carbon dioxide and free ammonia from the liquor While retaining the phe-A nols therein; (2) passing the het liquor from the distillation operation of step 1 in heat exchange relation With liquor coming from step 3, thus cool- -ing the liquor from step l; (3) vigorously agitating partially phenolized light oil and liquor coming from step 2, separating the partially dephenolzed liquor 4lrornthe completely phenolized light oil, vigorously agitating the partially dephenolized liquor and puried light oil and separating thev partially phenolized light oil from the dephenolized liquor; and (4) treating the completely phenolized light oil With caustic to form sodium phenolate, separating the sodium phenolate from oil and re-using the purified light oil. f

WILLIAM TIDDY. 

